1. Field of the Invention
This invention generally relates to a rolling-contact assembly, and, in particular, to a piggyback rolling-contact bearing assembly including an inner guide member having a U-shaped cross section and an outer guide member having a U-shaped cross section and provided as piggybacked to the inner guide member.
2. Description of the Prior Art
The rolling-contact bearing assembly is well known in the art and it is generally comprised of rolling elements interposed between an outer and inner guide member. When such a rolling-contact bearing assembly is used to support a rotating shaft, the inner and outer guide members are defined in the form of a ring. On the other hand, when such a rolling-contact bearing assembly is used for linear motion, the inner and outer guide members are defined in the form of a straight channel.
A typical example of such a linear motion rolling-contact bearing assembly is illustrated in FIGS. 4a-4c. As shown, the assembly includes a bed 1 which has a U-shaped cross section and corresponds to the inner guide member and a table 2 which has also a U-shaped cross section and corresponds to the outer guide member. In this assembly, the U-shaped bed 1 is provided right-side up with its open side located at its top, but the U-shaped table 2 is provided upside down with its open side located at its bottom, and, since the table 2 is larger in size than the bed 1, the table 2 effectively embraces the bed 1 from the front. The bed 1 is U-shaped and thus it has a flat bottom section and a pair of side wall sections each extending upright from the corresponding side of the bottom section. A straight, V-shaped guide groove 1a is formed along the outer surface of each of the side wall sections. Similarly, a corresponding straight, V-shaped guide groove 2a is formed along the inner surface of each of the side wall sections of the table 2. A plurality of balls 3 are provided as fitted between the opposed guide grooves 1a and 2a as equally spaced apart from each other by means of a ball retainer 4. With this structure, a straight, relative motion between the bed 1 and the table 2 may be produced as the balls 3 roll along the guide grooves 1a and 2a.
In the structure shown in FIGS. 4a-4c, there is also provided a table end plate 5 fixedly attached at each end of the table 2 by means of screws and a bed end plate 6 fixedly attached at each end of the bed 1 also by means of screws. A stopper 7 is fixedly attached to the inner surface of the flat, bottom section of the table 2 approximately at the center thereof, and, thus, the stroke of relative motion between the table 2 and the bed 1 is limited by the engagement between the stopper 7 and the bed end plate 6.
As described above, the rolling-contact bearing assembly typically includes the U-shaped inner and outer guide members 1 and 2, which are arranged such that the outer guide member 2 embraces the inner guide member 1 from the front whereby the inner surfaces of the flat, bottom sections of the inner and outer guide members 1 and 2 face opposed to each other. Such a structure is not advantageous from the viewpoint of space saving because a substantially large dead space is necessarily formed between the inner and outer guide members 1 and 2. Because of the presence of such a dead space, the assembly itself is relatively large in size, which limits the scope of application of such a bearing assembly. Moreover, it has been found difficult to make height H smaller in such a structure, which also presents another limitation to the scope of the application.